David Bradley is a science writer with a blog, who made a post about whiskey last December. It's pretty interesting. For example:

"Whisky lactone (3-methyl-4-octanolide) is present in oak, which is the most commonly used barrel material and endows whiskies with an essence of coconut aroma, while the diketone diacetyl (2,3-butanedione) gives the buttery aroma of most spirits. Commercially charred oaks used for aging barrels are particularly rich in phenols, with some 40 different phenolic compounds, having been revealed in charred oak barrels, each one of which can add to the flavour. The coumarin scopoletin is also present in whisky."